1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device having a fuse element used for instructing replacement of a defective memory cell with a spare cell, for example, in a dynamic random access memory (DRAM) of a large capacity.
2. Description of the Background Art
In a DRAM of a large capacity, it is extremely difficult to attain non-defectiveness in all memory cells. Therefore, generally, a redundant configuration, in which spare memory cells are provided in a memory cell array for replacing a defective portion, is adopted.
Japanese Patent Laying-Open No. 2001-210093 discloses a repair signal generating circuit used in a laser trimming scheme, in which a fuse unit corresponding to an address of a defective portion is blown with a laser beam to disconnect a circuit in the defective portion, and instead, a spare portion is operated.
In some cases, fuse blow by the laser beam is not completely achieved, which will cause a problem. That is, an internal circuit may determine that the fuse has not been blown, and an operation for replacement with the spare portion is not performed. Alternatively, a memory cell corresponding to a completely irrelevant address may be replaced.
A chip in which fuse blow has been incomplete and a current larger than a certain value flows exhibits malfunction always in a stable manner. Therefore, the chip can easily be removed in a test before shipping. On the other hand, if a small, remaining portion is present in a blown portion, an unstable operation may be exhibited, because the fuse is sometimes determined as blown and sometimes not blown, affected by complex operational factors such as operation timing, or operation temperature. It is difficult to remove the chip operating in such an unstable manner, and test conditions have had to be considered well.
Further, manufacturing yield has been lowered because of an error in replacement due to the presence of the small remaining portion.